This invention relates to a new class of polyoxyethylene modified epoxy resins and their preparation. Epoxy resins of this type are readily dispersable in water to provide useful coating compositions when cured.
The ever increasing need to reduce air pollution hazards caused by the volatilization of organic solvents has created an increased interest and importance in water-borne resin coating systems. This invention is directed to a new class of compounds that are useful for the preparation of aqueous based epoxy resin dispersions useful as coatings. Many of the dispersions of this invention do not require the use of any additional co-solvents. Other dispersions of this invention require significantly less of such co-solvents as compared to conventional epoxy resin coating systems.
U.S. Pat. No. 4,315,044 discloses an epoxy dispersion comprising an aqueous medium and a self-emulsifying epoxy resin which is the addition product of a liquid epoxy resin, a dihydric phenol such as bisphenol A and a diglycidyl ether of polyoxyalkylene glycol. These glycols are commercial Pluronic (BASF--Wyandotte) type surfactants which are block copolymers of ethylene oxide and propylene oxide having a molecular weight of 5000-10,000 containing about 50 to about 90 weight percent ethylene oxide and from about 10 to about 50 weight percent propylene oxide.
European Patent Application 0 202 765 utilizes essentially the same formulation as disclosed in U.S. Pat. No 4,315,044 but additionally requires approximately 8 weight percent of propylene glycol monomethyl ether as a co-solvent.
U.S. Pat. No. 4,154,709 discloses a modified epoxy resin in which no residual reactive epoxy groups remain. The system is essentially not an aqueous based system. Curing is achieved via the secondary hydroxyl groups with isocyanates.
European Patent Specification 0 109 173 discloses aqueous epoxy resin coating systems which are obtained by modifying the epoxy resin with a group of polyoxyalkylenediamine derivates prior to curing. The polyoxyalkylene diamines derivatives are known emulsifying agents which are block copolymers of ethylene oxide and propylene oxide that have been terminated with a primary amino group and which have a molecular weight of 900 to 5000.
Block copolymers with hydrophilic and hydrophobic block are also known. Au U.S. Pat. No. 4,173,693 discloses a water insoluble phase transfer catalyst comprising a polymer matrix of a water insoluble polymer bound to a poly alkylene glycol ether. The polymer matrices disclosed are based on styrene, styrene-divinyl benzene, styrene-glycoldimethylacrylate, urea-formaldehyde, aryl/polyamine-formaldehyde, phenol formaldehyde, polyacrylate and the like.
Lundberg U.S. Pat. No. 4,130,517 discloses multiphase block copolymers of hydrophilic blocks and hydrophobic blocks, wherein the copolymer must have an internal hydrophilic block. The hydrophilic blocks disclosed are based on ethylene oxide, acrylamide, alpha-hydroxy ethyl methacrylate, and vinylpyrolidone. The hydrophobic polymer blocks disclosed are selected from the group of styrene, t-butylstyrene, alpha-methyl styrene, vinyl toluene, methyl methacrylate, polyamides, methacrylonitrile, acrylonitrile monomers and polylactones.
Japan Kokai 7,494,786 discloses blending epoxy resins and/or unsaturated polyesters with nonionic surfactants, which contain polyethyleneoxide chains. Such blends are used to prepare organic solvent based coatings.
Hughes 3,799,797 discloses simultaneously crosslinking an epoxy resin with a diisocyanate and attaching to the epoxy resin a polyethylene glycol with a portion of the di-isocyanates. The epoxy resins provide scale resistant coatings.
The above mentioned references do not provide a means for emulsifying in water epoxy resins which are not naturally water emulsifiable. The references do not disclose a compound or composition which is effective in performing such emulsification.
What are needed are agents, compounds or compositions which can emulsify in water epoxy resins which are not emulsifiable in water. What are needed are water emulsions of epoxy resin which contain epoxy resins which are not self-emulsifiable. What are further needed are coatings prepared from water emulsions of standard epoxy resins.